Well, I'm not an expert but I've found that the regular handgunners aren't bad if you use them kinda like javelins that can fight. Don't put them in your front line - keep them in your second line or on the flanks. When your main line engages, try to run your handgunners around the flanks or back and get off a volley or two. When things get messy then charge your handgunners into the enemy - they have the stats to fight. Note that they have a short range and slow reload rate, so don't expect to be able to stand there and deliver volley-after volley, and never expect them to halt a charge - you'll be lucky if they get off one volley.

Couple of cautions: (1) If it's raining then your handgunners can't fire - makes using them on defense a bit of a gamble. (2) There is some muslim handgunner unit (Mamluk gunners?) that I've only bought as mercs, and they stink - stay away from them, they have no melee capabilities to speak of. (3) I don't really like the arquebus units. The gun is a little more effect than the handguns, but not a lot - and they have crappy melee - you'll get more use out of a good unit of arbelasts.

Oh - almost forgot - imo skirmish doesn't work very well with any missile unit that has a short range; you need to take your handgunners off of "fire at will" and skirmish and micromanage them a bit.

Hope this helps a bit. I'll be interested in what others have to offer, too.

Best wishes,